fix(git): surface non-git-repo as a typed error and align all panels via workspace state

Consolidate `.git` presence detection into a shared `git_repo` module used by both the workspace state watcher and the command preflight helper, replacing duplicated local definitions.

Introduce `AppErrorCode::NotAGitRepository` (HTTP 422) and preflight eleven frontend-callable git commands (log, status, list-branches, diff, diff-with-branch, show-diff, show-file, push-info, list-remotes, list-all-branches, commit-branches) so non-git folders short-circuit with a structured error instead of leaking locale-dependent git stderr.

Frontend `isNotAGitRepoError` checks the error code first and falls back to a multi-language regex list centralized in `src/i18n/git-error-patterns.ts`, covering the nine languages git actually translates into.

Wire the git log panel to `workspaceState.isGitRepo` rather than a local cached flag, so running `git init` or deleting `.git` externally propagates through the watcher and refreshes the panel automatically.

src/lib/app-error.ts

@@ -1,3 +1,4 @@
+import { NOT_A_GIT_REPO_PATTERNS } from "@/i18n/git-error-patterns"
 import type { AppCommandError } from "@/lib/types"
 
 type ObjectLike = Record<string, unknown>
@@ -46,11 +47,19 @@ export function extractAppCommandError(error: unknown): AppCommandError | null {
   }
 }
 
+// Must mirror `AppErrorCode::NotAGitRepository` in src-tauri/src/app_error.rs.
+// If the backend enum ever renames, both sides must change together.
+export const NOT_A_GIT_REPO_CODE = "not_a_git_repository"
+
 export function isNotAGitRepoError(error: unknown): boolean {
   const appError = extractAppCommandError(error)
+  if (appError?.code === NOT_A_GIT_REPO_CODE) return true
+
   const candidates = [appError?.detail, appError?.message]
   return candidates.some(
-    (text) => typeof text === "string" && /not a git repository/i.test(text)
+    (text) =>
+      typeof text === "string" &&
+      NOT_A_GIT_REPO_PATTERNS.some((pattern) => pattern.test(text))
   )
 }